This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Breast cancer is the most commonly diagnosed cancer and the second leading cause of cancer death in women. Unfortunately, no curative treatment exists for metastatic breast cancer. Early diagnosis of breast cancer provides the patients the best opportunities for cures or prolonged survival. Current [18F]FDG (2-[18F]fluoro-2-deoxy-D-glucose) PET (positron emission tomography) imaging has limited use by relatively low sensitivity and specificity. Novel and more effective imaging probes are urgently needed to improve the detection accuracy of primary, metastatic and recurrent breast cancers. Our strategy to improve the detection accuracy for breast cancer focuses on developing novel radiolabeled gonadotropin-releasing hormone (GnRH) peptides to target the GnRH receptors. GnRH receptor is a distinct molecular target in this project for developing more effective breast cancer-specific imaging probes due to its over-expression on human breast cancer cells and specimens. We will synthesize and evaluate a series of novel radiolabeled GnRH peptides in human breast cancer cells and xenografts in this project. Our central hypothesis and research design are strongly supported by our positive preliminary results. Positive results from this project will firstly demonstrate the feasibility of using the radiolabeled GnRH peptides for breast cancer imaging and provide new insight into the design of novel and more effective diagnostic and therapeutic agents for breast cancer.